On Monopolistic Competition and Optimal Product Diversity: a Comment on Cost Structure and Workers' Rents

In the Dixit-Stiglitz model of monopolistic competition, entry of firms is socially too small. Other authors have shown that excess entry is also a possibility with other preferences for diversity. We show that the cost structure and workers's rents can also explain excess entry.monopolistic competition; product diversity

Effect of Sr substitution on superconductivity in Hg2(Ba1-ySry)2YCu2O8-d (part2): bond valence sum approach of the hole distribution

The effects of Sr substitution on superconductivity, and more particulary the changes induced in the hole doping mechanism, were investigated in Hg2(Ba1-ySry)2YCu2O8-d by a "bond valence sum" analysis with Sr content from y = 0.0 to y = 1.0. A comparison with CuBa2YCu2O7-d and Cu2Ba2YCu2O8 systems suggests a possible explanation of the Tc enhancement from 0 K for y = 0.0 to 42 K for y = 1.0. The charge distribution among atoms of the unit cell was determined from the refined structure, for y = 0.0 to 1.0. It shows a charge transfer to the superconducting CuO2 plane via two doping channels pi(1) and pi(2), i.e. through O2(apical)-Cu and Ba/Sr-O1 bonds respectively.Comment: 13 pages, 5 figures, accepted for publication in Journal of Physics: Condensed Matte

High frame rate contrast enhanced echocardiography: microbubbles stability and contrast evaluation

Contrast Echocardiography (CE) with microbubble contrast agents have significantly advanced our capability in assessing cardiac function, including myocardium perfusion imaging and quantification. However in conventional CE techniques with line by line scanning, the frame rate is limited to tens of frames per second and image quality is low. Recent works in high frame-rate (HFR) ultrasound have shown significant improvement of the frame rate. The aim of this work is to investigate the MBs stability and the contrast improvement using HFR CE compared to CE transmission at an echocardiography relevant frequency for different mechanical indices (MIs). Our results show that the contrast and bubble destruction of HFR CE and standard CEUS varies differently as a function of space and MIs. At low MIs, HFR CE shows a similar behavior as focused CE with little MB destruction, and generates better CTR (up to 3 folds). As MI increases, the MB destruction is more significant for HFR CE with a reduction of the CTR

Recrystallization of silicon by pulsed lasers

Calculation of the evolution of temperature during pulsed laser annealing has been performed. The results are presented in directly useful figures for the two kinds of laser generally used (YAG, Ruby). The results are compared to various experimental measurements performed by RBS. If the crystallographic quality is quite good, TSC and DLTS measurements have shown that electrically active defects are still present after laser annealing

DEPTH MEASUREMENT OF THE PHASE CHANGE UNDER PULSED RUBY LASER ANNEALING

Irradiation of crystalline silicon by pulsed ruby laser induces a surface phase change. A direct measurement of the maximum thickness phase change is reported. Successful comparison with a thermal model is done

Mesures de vies moyennes par effet Doppler

Des vies moyennes de niveaux nucléaires ont été déterminées par la méthode de l'effet Doppler. Les rayonnements gamma de désexcitation ont été détectés dans des compteurs Ge(Li). Des vies moyennes ont été obtenues pour les niveaux 0,953 MeV de 12B et 6,44 MeV de 14N

Direct observation of the influence of the As-Fe-As angle on the Tc of superconducting SmFeAsO1−x_{1-x}Fx_{x}

The electrical resistivity, crystalline structure and electronic properties calculated from the experimentally measured atomic positions of the compound SmFeAsO$_{0.81}$F$_{0.19}$ have been studied up to pressures ~20GPa. The correlation between the pressure dependence of the superconducting transition temperature (Tc) and crystallographic parameters on the same sample shows clearly that a regular FeAs$_{4}$ tetrahedron maximizes Tc, through optimization of carrier transfer to the FeAs planes as indicated by the evolution of the electronic band structures.Comment: 15pages, 4 figure

High pressure x-ray diffraction study of the volume collapse in Ba24Si100 clathrate

International audienceThe high pressure stability of the silicon type-III clathrate Ba24Si100 has been studied by x-ray diffraction (XRD) up to a maximum pressure of 37.4 GPa. The high pressure behavior of this Si type-III clathrate appears to be analogous to the structural type-I parent Ba8Si46. An isostructural volume collapse is observed at ~23 GPa, a value higher than for Ba8Si46 (13-15 GPa). The crystallinity of the structure is preserved up to the maximum attained pressure without amorphization, which appears to be in contradiction with the interpretation given in a Raman spectroscopy study [Shimizu et al., Phys. Rev. B 71, 094108 (2005)]. Nevertheless, the XRD analysis shows the appearance of a type-III disordered nanocaged-based crystalline structure after the volume collapse. Moreover, we find that the volume collapse transformation is (quasi)reversible after pressure release. Additionally, a low pressure transition first evidenced by Raman spectroscopy is also observed in our XRD study at 5 GPa: The variation of the isotropic thermal factors of Ba atoms shows a clear discontinuity at this pressure while the average positions of Ba atoms remain identical

INTERACTION BETWEEN ARGON AND DOPANTS IN SPUTTERED a-Si : H

The concentrations of As, B, H, Ar and Si in sputtered a-Si : H are measured by helium Rutherford backscattering and nuclear reactions analysis. Excess or deficit of hydrogen and argon by comparison with intrinsic a-Si : H are found in presence of dopants at high deposition rate. This is related to the plasma deposition method and would suggest micro grain structure in the deposited layer